This is also not a valid solution due to MVVM concerns. Because the code behind is moved to the ViewModel. But the ViewModel now knows about View details (e.g. grids, columns, comboboxes, events, ...).

The better way would be to enable the eventhandler View_RecordPropertyChanged to get the data without casting to a class defined in the model. So the data could be sent to ViewModel via Messenger and the rest of data handling will be done there.

For example in Grid_CurrentCellValidated I'm able to read the data in a comfort way:

We regret to inform you that, the e.OldValue and e.NewValue are not in View_RecordPropertyChanged eventhandler like in Grid_CurrentCellValidated. Could you please maintain the list for adding a new row with ItemType = "nonregular" and an empty ValueType inyour application.